Fuel injection apparatus for internal combustion engine

ABSTRACT

A fuel injection apparatus has an accumulator, a booster, a nozzle, a hydraulic circuit, a hydraulic pressure valve and a control valve. At least one of a transmission path, which is connected to the hydraulic circuit, and the hydraulic piston is configured to generate a delay in an operation of the nozzle or the booster that is driven by one of fuel pressure in the control chamber and fuel pressure in the back pressure chamber that is directly controlled by the control valve, against an operation of the booster or the nozzle that is driven by the other of the fuel pressure in the back pressure chamber and the fuel pressure in the control pressure indirectly controlled by the hydraulic pressure valve.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority ofJapanese Patent Application No. 2004-337817 filed on Nov. 22, 2004, thecontent of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a fuel injection apparatus for aninternal combustion engine, specifically for a diesel engine.

BACKGROUND OF THE INVENTION

Conventionally a common rail system is known as a fuel injectionapparatus for an internal combustion engine. The common rail system isprovided with an accumulator (a common rail) that accumulates fueltherein at a specific pressure, and injects high pressure fuel suppliedfrom the accumulator via an injector into a cylinder of the internalcombustion engine. The common rail system has an excellent performancethat can independently control an injection pressure and an injectionamount from each other. It is demanded recently to improve theperformance of the common rail system further to make exhaust gas cleanand to improve a fuel consumption performance. U.S. Pat. No. 5,622,152and its counterpart JP-2885076-B2 disclose a fuel injection apparatus tosatisfy this demand in a simple fashion

The fuel injection apparatus disclosed in U.S. Pat. No. 5,622,152 isprovided with; a hydraulic control mechanism for opening and closing thenozzle, which is an advantage of the common rail system; and a pressureincreasing mechanism to increase a fuel pressure in the accumulator. Thepressure increasing mechanism enables fuel injection at still higherpressure, and both of pressure increasing control and fuel injectioncontrol. As a result, the fuel injection apparatus can change fuelinjection pressure during one injection cycle, to realize a microinjection at a low pressure and a main injection at a super highpressure, and to optimize a pattern of an injection ratio. Accordingly,further minute optimization of fuel combustion is achieved.

In the above-mentioned fuel injection apparatus disclosed in U.S. Pat.No. 5,622,152, however, it is substantially necessary to independentlycontrol two operations, that is, the pressure increasing operation andthe fuel injection operation from each other. Thus, the fuel injectionapparatus requires at least two actuators, for example, to make aconstruction of the system intricate, and to increase a manufacturingcost thereof.

In this regard, JP-2003-106235-A2 discloses another fuel injectionapparatus that can achieve functions equivalent to those of theabove-mentioned fuel injection system (disclosed in U.S. Pat. No.5,622,152 and JP-2885076-B2).

FIG. 11 depicts a hydraulic circuit of the fuel injection apparatusdisclosed in JP-2003-106235-A2. The fuel injection apparatus has acontrol valve 100 that is driven by one actuator. The control valve 100is connected via a fuel passage 130 to a booster 110, via a fuel passage140 to a nozzle 120, and via a fuel passage 150 to an accumulator 160.The control valve 100 is provided with: a hydraulic pressure port 101that is connected to the fuel passages 130, 140; and a low pressure port102 that is connected to a low pressure side drain passage 170. A valvebody 103 is driven between: a valve closing position (the position shownin FIG. 11) to block a communication between the hydraulic pressure port101 and the low pressure port 102; and a valve opening position to allowthe communication between the hydraulic pressure port 101 and the lowpressure port 102.

When the valve body 103 is driven to the valve closing position, fuelpressure in the accumulator 160 is transmitted to a control chamber 111of the booster 110 and a back pressure chamber 121 of the nozzle 120. Inthe booster 110 in this time, the hydraulic pressure is in balancebetween an upstream and downstream sides of a hydraulic piston 112,which is installed in the booster 110. Thus, the pressure of the fuel,which is supplied from the accumulator 160 via a fuel passage 180 to thepressure increase chamber 113, does not increase. Concurrently, in thenozzle 120, a needle (not shown), which is installed therein andreceives the fuel pressure in the back pressure chamber 121, keeps avalve closing state, not to perform fuel injection.

When the valve body 103 is driven to the valve opening position, thehydraulic pressure port 101 and the low pressure port 102 of the controlvalve 100 is communicated with each other, so that the fuel pressure inthe control chamber 111 and in the back pressure chamber 121 is releasedvia the control valve 100 to a lower pressure side. Thus, in the booster110, the hydraulic pressure comes out of balance between the upstreamand downstream sides of the hydraulic piston 112, to move the hydraulicpiston 112 downward in the figure, so that the pressure of the fuel inthe pressure increase chamber 113 increases, and the fuel is supplied tothe nozzle 120. In the nozzle 120, a fuel pressure decrease in the backpressure chamber 121 lifts the needle upward, to inject the super highpressure fuel supplied from the booster 110.

In the above-mentioned fuel injection apparatus disclosed inJP-2003-106235-A2, the control chamber 111 of the booster 110 and theback pressure chamber 121 of the nozzle are connected to the accumulator160 at all times. That is, the control chamber 111 and the back pressurechamber 121 are respectively in communication with the accumulator 160at all times regardless of a valve opening and closing state of thecontrol valve 100. Accordingly, the fuel passages 130, 140 and 150 arerespectively provided with apertures 190, 200 and 210. However, it isdifficult to optimize controls of the booster 110 and the nozzle 120because of an interaction among the apertures 190, 200 and 210.

SUMMARY OF THE INVENTION

The present invention is achieved in view of the above-described issues,and has an object to provide a fuel injection apparatus for an internalcombustion engine that is able to control a pressure increase operationby a booster and an injection operation by a nozzle with high accuracy,and to secure enough control flexibility with one actuator.

The fuel injection apparatus has an accumulator, a booster, a nozzle, ahydraulic circuit, a hydraulic pressure valve and a control valve. Theaccumulator accumulates fuel therein at a predetermined pressure. Thebooster is provided with a control chamber in which fuel pressurechanges in accordance with a fuel inflow into the control chamber and afuel outflow out of the control chamber. The booster is further providedwith a hydraulic piston that moves in accordance with a change of thefuel pressure in the control chamber. The booster pressurizing the fuelsupplied from the accumulator in accordance with a pressurizingoperation of the hydraulic piston. The nozzle is provided with a backpressure chamber in which fuel pressure changes in accordance with afuel inflow into the back pressure chamber and a fuel outflow out of theback pressure chamber. The nozzle is further provided with a needle thatmoves in accordance with a change of the fuel pressure in the backpressure chamber. The nozzle injects the fuel supplied from theaccumulator or the fuel pressurized by the booster in accordance with avalve opening operation of the needle. The hydraulic circuit is providedwith a fuel passage for transmitting the fuel pressure in theaccumulator to the back pressure chamber, and a fuel passage forreleasing the fuel pressure in the back pressure chamber to a lowpressure system. The hydraulic pressure valve is provided with a valvebody that is disposed in the fuel passage communicated with the controlchamber or disposed in a fuel passage communicated with the backpressure chamber to open and block the fuel passage to control anoperation of the valve body in accordance with the fuel pressure that istransmitted via a transmission path connected to the hydraulic circuit.The control valve is provided with a valve body that is driven by atwo-position actuator. The valve body connects any one of a highpressure side communicated the accumulator and the low pressure systemcommunicated with a fuel tank to the hydraulic circuit, to control thehydraulic circuit, and to control the fuel pressure transmitted to thehydraulic pressure valve. One of the fuel pressure in the controlchamber and the fuel pressure in the back pressure chamber is directlycontrolled by the control valve. The other of the fuel pressure in thecontrol chamber and the fuel pressure in the back pressure chamber isindirectly controlled via the hydraulic pressure valve, to control anoperation of the booster and an operation of the nozzle.

At least one of the transmission path and the hydraulic piston isconfigured to generate a delay in an operation of the nozzle or thebooster that is driven by the one of the fuel pressure in the controlchamber and the fuel pressure in the back pressure chamber directlycontrolled by the control valve, against an operation of the booster orthe nozzle that is driven by the other of the fuel pressure in the backpressure chamber and the fuel pressure in the control pressureindirectly controlled by the hydraulic pressure valve.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will beappreciated, as well as methods of operation and the function of therelated parts, from a study of the following detailed description, theappended claims, and the drawings, all of which form a part of thisapplication. In the drawings:

FIG. 1 is a hydraulic circuit diagram of a fuel injection apparatusaccording to a first embodiment of the present invention;

FIG. 2 is a detailed hydraulic circuit diagram system of the fuelinjection apparatus according to the first embodiment, which includes aspecific construction of a control valve and a hydraulic pressure valve;

FIG. 3 is another hydraulic circuit diagram of a fuel injectionapparatus according to a first embodiment of the present invention;

FIG. 4 is still another hydraulic circuit diagram of a fuel injectionapparatus according to a first embodiment of the present invention;

FIG. 5 is a schematic cross-sectional view showing an entireconstruction of a fuel injection valve in the fuel injection apparatusaccording to the first embodiment;

FIG. 6 is a timing chart showing an operation of the fuel injectionapparatus according to the first embodiment;

FIG. 7 is a graph showing an operation of the fuel injection apparatusaccording to the first embodiment, which is calculated by a computersimulation;

FIG. 8 is a hydraulic circuit diagram of a fuel injection apparatusaccording to a second embodiment of the present invention;

FIG. 9 is a hydraulic circuit diagram of a fuel injection apparatusaccording to a third embodiment of the present invention;

FIG. 10 is a hydraulic circuit diagram of a fuel injection apparatusaccording to a fourth embodiment of the present invention; and

FIG. 11 is a hydraulic circuit diagram of a conventional fuel injectionapparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

FIG. 1 depicts a hydraulic circuit of a fuel injection apparatusaccording to a first embodiment of the present invention. FIGS. 2-4respectively depict the hydraulic circuit in detail and show specificconstructions of a control valve and a hydraulic pressure valve in thefuel injection apparatus.

The fuel injection apparatus 1 according to the first embodiment isapplied to a common rail system of a diesel engine for a vehicle, forexample. As shown in FIG. 1, the fuel injection apparatus 1 is providedwith: an accumulator 2 for accumulating fuel therein at a specificpressure; a booster 3 for increasing the pressure of the fuel that issupplied from the accumulator 2; a nozzle 4 for injecting the fuel thatis supplied from the accumulator 2 or the fuel whose pressure isincreased by the booster 3; a control valve 5 for controlling anoperation of the booster 3 and an operation of the nozzle 4; and so on.The components except the accumulator 2, that is, the booster 3, thenozzle 4, the control valve 5, etc. constitutes a fuel injection valve 6as shown in FIG. 5.

The accumulator 2 is connected by a fuel pipe 7 to the fuel injectionvalve 6 to supply the fuel, which is accumulated in the accumulator 2,via the fuel pipe 7 to the fuel injection valve 6. The booster 3 has ahydraulic piston 8, in which a large diameter piston 8 a and a smalldiameter plunger 8 b are coaxially provided. The hydraulic piston 8 isslidably installed in a large diameter bore and a small diameter bore,which are formed in a booster body 9 (refer to FIG. 5). In the largediameter bore, which installs the large diameter piston 8 a therein,provides: a driving chamber 10 over an upper end face of the largediameter piston 8 a; and a control chamber 11 below a lower end face ofthe large diameter piston 8 a. In the small diameter bore, whichinstalls the small diameter plunger 8 b therein, provides a pressurizingchamber 12 below a lower end face of the small diameter plunger 8 b.

The driving chamber 10 is connected via the fuel passage 13 to the fuelpipe 7, and supplied with the fuel pressure in the accumulator 2 via thefuel pipe 7 and the fuel passage 13. The fuel pressure in the drivingchamber 10 acts on the upper end face of the hydraulic piston 8, to urgethe hydraulic piston 8 downward.

The control chamber 11 is connected via a round passage constituting apart of the hydraulic circuit, which is described later, to a switchingport 40 of the control valve 5 (the round passage and the switching port40 are described later). The control valve 5 controls the fuel pressurein the control chamber 11. In the control chamber 11 is disposed aspring 14, as shown in FIG. 5, to urge the hydraulic piston 8 upward inthe drawing.

The round passage is composed of two fuel passages 15, 16, which connectthe switching port 40 of the control valve 5 in parallel with thecontrol chamber 11 as shown in FIG. 1. One fuel passage 15 is providedwith a check valve 17 that allows a fuel flow from the control valve 5to the control chamber 11 and prevents a backward fuel flow. The otherfuel passage 16 is provided with a hydraulic pressure valve 18, which isdescribed below. The two fuel passages 15, 16 may be independent fromeach other over their entire length from one end connected to theswitching port 40 of the control valve 5 to the other end connected tothe control chamber 11. Alternatively, as shown in FIG. 1, the one endside portion and the other end side portion of the two fuel passages 15,16 may be integrally formed.

The pressurizing chamber 12 is connected via a fuel passage 20 having acheck valve 19 to the above-mentioned fuel pipe 7, and via a fuelpassage 21 to a oil accumulator 4 a provided in the nozzle 4 (refer toFIG. 5). The check valve 19 allows a fuel flow toward the pressurizingchamber 12 in the fuel passage 20, that is, a flow of the fuel suppliedfrom the accumulator 2, and prevents a backward flow, that is, a fuelflow toward the accumulator 2. Thus, the fuel pressure in theaccumulator 2 is transmitted to the pressurizing chamber 12, and via thefuel passage 21 to the oil accumulator 4 a of the nozzle 4.

As shown in FIG. 5, the nozzle 4 is composed of: a nozzle body 23, at aleading end of which is formed an injection hole 22; a needle 24, whichis installed in the nozzle body 23; a nozzle holder 26, which forms aback pressure chamber 25 over the needle 24 in the figure; and so on.The nozzle 4 is disposed below the booster body 9 and fastened by aretainer 27 to the booster body 9. In the nozzle body 23 is formed anannular fuel passage 28 to surround the needle 24, and theabove-mentioned oil accumulator 4 a at an upstream end of the fuelpassage 28. Further, a conical sheet face (not shown) is formed betweenthe fuel passage 28 and the injection hole 22.

The back pressure chamber 25 is connected via a fuel passage 29constituting a part of the hydraulic circuit to the switching port 40 ofthe control valve 5, so that the control valve 5 controls the fuelpressure in the back pressure chamber 25. The fuel passage is providedwith an aperture 30. When the fuel pressure in the accumulator 2 istransmitted to the back pressure chamber 25, the needle 24 receives thefuel pressure in the accumulator 2 and a restitutive force of a spring31, which is installed in the back pressure chamber 25 (refer to FIG.5), to be urged in a valve closing direction, that is, downward in FIG.5. Thus, a sheet line (not shown), which is provided on a leading endportion of the needle 24, seats on the above-mentioned seat face, toblock a communication between the fuel passage 28 and the injection hole22. When the fuel pressure in the back pressure chamber 25 is releasedby the control valve 5, the needle 24 lifts up to allow thecommunication between the fuel passage 28 and the injection hole 22.Then, the fuel supplied to the oil accumulator 4 a passes through thefuel passage 28 and is injected out of the injection hole 22.

As shown in FIG. 5, the control valve 5 has: a valve chamber 5 a, whichis formed in a control valve body 32; valve body 5 b, which is installedin the valve chamber 5 a; and a two-position actuator 33 for driving thevalve body 5 b. The control valve 5 is disposed on the booster body 9and fastened by a retainer 34 to the booster body 9. As shown in FIG. 2,the valve chamber 5 a is provided with: a input port 36, through whichthe fuel pressure in the accumulator 2 is supplied to the valve chamber5 a via a fuel passage 35 that is connected to the fuel pipe 7; a lowpressure port 39, which is connected via a drain passage 37 to a fueltank 38; a first switching port, which is connected via theabove-mentioned round passage (the fuel passages 15, 16) to the controlchamber 11 of the booster 3; and the second switching port, which isconnected via the fuel passage 29 to the back pressure chamber 25 of thenozzle 4. The first and second switching ports are described as answitching port 40 in the following.

The valve body 5 b switches between: a fuel pressure transmission mode(a position shown in FIGS. 1, 2 and 5) to interrupt a communicationbetween the low pressure port 39 and the switching port 40 and to allowa communication between the input port 36 and the switching port 40; anda fuel pressure release mode (a position shown in FIGS. 3 and 4) tointerrupt the communication between the input port 36 and the switchingport 40 and to allow the communication between the low pressure port 39and the switching port 40. That is, the control valve 5 is atwo-position three way valve to switch a fuel flow direction inaccordance with an operation mode.

As shown in FIG. 2, the two-position actuator 33 is composed of: adisk-shaped armature 41, which is connected to the valve body 5 b; anelectromagnetic coil 43, which is electrically controlled by an electriccontrol unit (ECU) 42 mounted on the vehicle; a return spring 44 forurging the armature 41 downward in the drawing; and so on. When anelectric power supply to the electromagnetic coil 43 is on, thetwo-position actuator 33 generates an electromagnetic force. Theelectromagnetic force draws the armature 41 upward in the figure againsta restitutive force of the return spring 44, to generate a drivingforce. When the electric power supply to the electromagnetic coil 43 isstopped, the electromagnetic force disappears. In accordance with theelectromagnetic force disappear, the restitutive force of the returnspring 44 pushes the armature 41 back to an initial state shown in FIG.2. The hydraulic circuit diagram of FIG. 2 shows an operationaldirection of the armature 41 in an opposite orientation from that inFIG. 5. That is, the energized the electromagnetic coil 43 generates theelectromagnetic force to move the armature 41 downward in FIG. 5, andupward in FIG. 2.

As shown in FIG. 2, the above-mentioned hydraulic pressure valve 18 iscomposed of: a valve chamber 18 a; the valve body 18 b, which isinstalled in the valve chamber 18 a; a spring 18 c for urging the valvebody 18 b; and so on. The valve chamber 18 a is provided with: an inletport 45, which is communicated to the control chamber 11 of the booster3; and an outlet port 46, which is communicated to the switching port 40of the control valve 5. The valve body 18 b switches between: a valveclosing mode (a position shown in FIGS. 1, 2 and 5) to interrupt acommunication between the inlet port 45 and the outlet port 46; and avalve opening mode (a position shown in FIG. 4) to allow thecommunication between the inlet port 45 and the outlet port 46. Thespring 18 c is installed in an operation chamber 18 d, which is providedin a lower portion of the valve chamber 18 a in a depressed manner, tourge the valve body 18 b in a valve closing direction (upward in FIG.2).

To the hydraulic pressure valve 18 is transmitted the fuel pressure inthe accumulator 2 at all times via a branch passage 47, which isbranched from the fuel passage 35. The fuel pressure in the hydraulicpressure valve 18 urges the valve body 18 b in a valve opening direction(downward in FIG. 2). To the operation chamber 18 d is transmitted afuel pressure at a magnitude in accordance with an operation mode of thecontrol valve 5 via a pressure transmission path 48, which is connectedto the switching port 40 of the control valve 5. That is, when thecontrol valve 5 is set to the fuel pressure transmission mode, the fuelpressure in the accumulator 2 is transmitted via the pressuretransmission path 48 to the operation chamber 18 d. Then, a differencebetween a force to urge the valve body 18 b in the valve openingdirection and a force to urge the valve body 18 b in the valve closingdirection decreases or is equalized. In this manner, the restitutiveforce of the spring 18 c urges the valve body 18 b in the valve closingdirection, to set the control valve 5 to the valve closing mode.

When the control valve 5 is set to the fuel pressure release mode, theoperation chamber 18 d is communicated with a low pressure side, and apressure difference acting on the valve body 18 b increases (the forceto urge the valve body 18 b in the valve opening direction becomeslarger than the force to urge the valve body 18 b in the valve closingdirection). Then, the valve body 18 b is urged in the valve openingdirection against the restitutive force of the spring 18 c, to be set tothe valve opening mode. That is, the hydraulic pressure valve 18 is atwo-position two way valve to open and close the fuel passage 16 inaccordance with an operation mode.

In the first embodiment, the pressure transmission path 48 is providedwith an aperture 49 as shown in FIG. 1. Thus, when the control valve 5is switched from the fuel pressure transmission mode to the fuelpressure release mode, the aperture 49 generates a specific length oftime lag in switching the hydraulic pressure valve 18 from the valveclosing mode to the valve opening mode. The aperture 49 is configured togenerate the specific length of the time lag.

An operation of the fuel injection apparatus is described in thefollowing referring to FIGS. 2 to 4 and a timing chart shown in FIG. 6.States 1, 2 and 3 in FIG. 6 respectively correspond to the states shownin FIGS. 2, 3 and 4. When the electromagnetic coil 43 of thetwo-position actuator 33 is OFF, as shown in FIG. 2, the control valve 5is set to the fuel pressure transmission mode. The fuel pressuretransmission mode blocks the communication between the switching port 40and the low pressure port 39, and allows the communication between theinput port 36 and the switching port 40. Thus, the fuel pressure in theaccumulator 2 is transmitted to the switching port 40. The fuel pressurein the accumulator is transmitted via the pressure transmission path 48to the operation chamber 18 d, so that the hydraulic pressure valve 18is set to the valve closing mode.

Accordingly, the fuel pressure in the accumulator 2 is transmitted viathe one fuel passage 15 to the control chamber 11 of the booster 3, andalso via the fuel passage 29 to the back pressure chamber 25 of thenozzle 4. In the booster 3 in this time, the fuel pressure in theaccumulator 2 is also transmitted to the driving chamber 10 and to thepressurizing chamber 12, to balance the fuel pressure acting on both ofan upper and lower end faces of the hydraulic piston 8 with each other.As a result, the spring 14 (refer to FIG. 5) urges the hydraulic piston8 upward in the figure. Thus, a volume of the pressurizing chamber 12gradually increases, to fill the fuel in the pressurizing chamber 12 inaccordance with the volume increase of the pressurizing chamber 12. Inthis state, the fuel pressure in the back pressure chamber 25 of thenozzle 4 is equal to that in the accumulator 2, so that the needle 24does not lift up. Thus, the communication between the fuel passage 28and the injection hole 22 in the nozzle 4 is kept blocked, and no fuelis injected.

Next, the ECU 42 outputs a driving signal to the two-position actuator33 to energize the electromagnetic coil 43. Then, as shown in FIG. 3,the control valve 5 is switched from the fuel pressure transmission modeto the fuel pressure release mode. The fuel pressure release mode blocksthe communication between the input port 36 and the switching port 40,and allows the communication between the switching port 40 and the lowpressure port 39. Thus, the back pressure chamber 25 of the nozzle 4 iscommunicated with the low pressure side, to release the fuel pressure inthe back pressure chamber 25. Then, the needle 24 lifts up, and the fuelsupplied to the oil accumulator 4 a is injected out of the injectionhole 22. In this time, the hydraulic pressure valve 18 is kept to thevalve closing mode shown in FIG. 3 until the fuel pressure in the backpressure chamber 25 decreases to a specific pressure, so that thehydraulic piston 8 does not concurrently move with the fuel pressurerelease in the back pressure chamber 25. Accordingly, an injectionpressure of the nozzle 4 is not equal to a super high pressure, which isincreased by the booster 3, but approximately equal to the fuel pressurein the accumulator 2.

Then, the fuel pressure in the back pressure chamber 25 decreases to thespecific pressure. Further, the hydraulic pressure valve 18 is switchedfrom the valve closing mode to the valve opening mode in the specificlength of the time lag configured by the aperture 49 of the pressuretransmission path 48 as shown in FIG. 4. Thus, the control chamber 11 ofthe booster 3 is connected via the hydraulic pressure valve 18 to theswitching port 40 of the control valve 5, to release the fuel pressurein the control chamber 11 to the lower pressure side. As a result, thefuel pressure acting on both of an upper and lower end faces of thehydraulic piston 8 get out of balance with each other. Accordingly, thefuel pressure in the driving chamber 10 urges the hydraulic piston 8downward.

In accordance with the movement of the hydraulic piston 8, the fuelpressure in the pressurizing chamber 12 start increasing. Ultimately,the fuel pressure in the pressurizing chamber 12 is increased inaccordance with a cross-sectional area ration of the large diameterpiston 8 a to the small diameter plunger 8 b. For example, when the fuelpressure in the accumulator 2 is set to 50 MPa, and a cross-sectionalarea ratio of the large diameter piston 8 a to the small diameterplunger 8 b is set to 4:1, the fuel pressure in the pressurizing chamber12 will be (4×50=) 200 MPa. Accordingly, the super high pressure, thepressure of which is increased by the booster 3, is injected out of thenozzle 4.

Subsequently, when the electric power supply to the electromagnetic coil43 is stopped at a specific timing (when an injection amount reaches aspecific value, for example), the control valve 5 is switched from thefuel pressure release mode to the fuel pressure transmission mode. Thus,the fuel pressure in the accumulator 2 is transmitted to the backpressure chamber 25 of the nozzle 4 and to the control chamber 11 of thebooster 3. Accordingly, in the nozzle 4, the fuel pressure in the backpressure chamber 25 increases, to push the needle 24 back to stop theinjection. In the booster 3, the fuel pressure in the control chamber 11increases, so that the hydraulic piston 8 immediately stops a pressureincreasing operation and starts a return process.

FIG. 7 depicts an operation of the fuel injection apparatus 1 accordingto the first embodiment, which is calculated by a computer simulation.In the simulation, the cross-sectional area ratio is set to 2:1. Thesimulation supports the above-described operations and performances ofthe fuel injection apparatus 1.

The fuel injection apparatus 1 according to the first embodiment isprovided with the two fuel passages 15, 16 that connect the switchingport 40 of the control valve 5 in parallel with the control chamber 11.Thus, a different path is used in a case to release the fuel pressure inthe control chamber 11 from a case to increase the fuel pressure. Thatis, in increasing the fuel pressure in the control chamber 11, the fuelpressure in the accumulator 2 is transmitted to the control chamber 11via the one fuel passage 15 provided with the check valve 17. Inreleasing the fuel pressure in the control chamber 11, the fuel pressureis released to a lower pressure side via the other fuel passage 16provided with the hydraulic pressure valve 18.

According to the above-described construction, the fuel pressure in thecontrol chamber 11 slowly decreases slower by providing the other fuelpassage 16 with an aperture (not shown). Thus, as represented by abroken line A in FIG. 6, it is possible to modify a pressure increasespeed of the booster 3 (a moving speed of the hydraulic piston 8).Alternatively, the fuel pressure in the control chamber 11 slowlydecreases by providing the one fuel passage 15 with an aperture (notshown). Thus, as represented by a broken line B in FIG. 6, it ispossible to modify the pressure decrease speed of the booster 3 (themoving speed of the hydraulic piston 8).

Further, in the first embodiment, the pressure transmission path 48,which is connected to the operation chamber 18 d of the hydraulicpressure valve 18, is provided with the aperture 49. Thus, it ispossible to delay a timing for the hydraulic pressure valve 18 to beswitched from the valve closing mode to the valve opening mode.Accordingly, as represented by a broken line C in FIG. 6, it is possibleto apply a time lag to a timing to start operating the booster 3 (tostart the pressure increase). In this manner, it is possible to optimizean injection ratio patterns in accordance with a driving condition ofthe internal combustion engine, by modifying the pressure increasingspeed of the booster 3, the pressure decreasing speed of the booster 3,and the starting timing of the pressure increase of the booster 3. Ascommonly known, the optimization of the injection patterns is effectivefor exhaust gas cleaning and output power increase. In addition, bymodifying the pressure decreasing speed of the booster 3, it is possibleto perform such settings as to initialize the injection ratio regardlessof other properties, especially in a high-speed internal combustionengine.

Furthermore, by delaying the pressure increase starting timing, it ispossible to set an initial injection pressure to a small value and tomodify the duration time of the initial injection by the aperture 49.Specifically, in a micro injection, which does not require a super highfuel pressure, a time to the injection state is quite small, so that itis possible to inject the fuel at a non-increased pressure (at the fuelpressure in the accumulator 2).

In the fuel injection apparatus 1 according to the first embodiment, afuel leakage does not occur except a switching leakage, which slightlyoccurs in switching the operation modes of the control valve 5, so thatit is possible to limit an energy loss, and to improve a fuelconsumption performance of the internal combustion engine. Further, thetwo fuel passages 15, 16 connect the control valve 5 in parallel withthe control chamber 11 of the booster 3, so that the pressure increasestep finishes at the same time as the injection finishes. Thus, it ispossible to decrease a wasteful operation of the booster 3, not to wastea driving energy.

Modification of the First Embodiment

In the first embodiment, the pressure transmission path 48 is providedwith the aperture 49, to delay the timing for the hydraulic pressurevalve 18 to be switched from the valve closing mode to the valve openingmode. Thus, a time lag is applied to the operation start of the booster3 (to the pressure increase start timing). Alternatively, instead of theaperture 49, it is possible to adjust the time lag by adequately settingan operation pressure of the hydraulic pressure valve 18. For example,the time lag can be modified also by adjusting a load of the spring 18 cto urge the valve body 18 b of the hydraulic pressure valve 18. The timelag to operate the hydraulic pressure valve 18 can be delayed also by acooperative operation of an effect of the aperture 49 provided in thepressure transmission path 48 and an operation pressure of the hydraulicpressure valve 18.

Second Embodiment

FIG. 8 depicts a hydraulic circuit of the fuel injection apparatus 1according to a second embodiment of the present invention.

The fuel injection apparatus 1 according to the second embodimentdiffers from the first embodiment in a construction of passages toconnect the hydraulic pressure valve 18 to the outlet port 46. That is,in the first embodiment, the outlet port 46 of the hydraulic pressurevalve 18 is connected to the switching port 40 of the control valve 5.In the second embodiment, as shown in FIG. 8, the outlet port 46 of thehydraulic pressure valve 18 is connected via an outlet passage 50 (apart of the second fuel passage) to the drain passage 37. Thus, when indischarging a relatively large amount of the fuel out of the controlchamber 11 of the booster 3 in a short time, the fuel do not passthrough the control valve 5. Thus, it is possible to downsize thecontrol valve 5.

The pressure transmission path 48, which is connected to the operationchamber 18 d of the hydraulic pressure valve 18 (refer to FIG. 2), isprovided with the aperture 49. By an effect of the aperture 49 and/or anoperation pressure of the hydraulic pressure valve 18, it is possible toapply a time lag to a timing to start operating the booster 3 (to startthe pressure increase), in the same manner as in the first embodiment.

Third Embodiment

FIG. 9 depicts a hydraulic circuit of a fuel injection apparatus 1according to a third embodiment of the present invention.

The fuel injection apparatus 1 according to the third embodiment is anexample in which an inflow passage 51 (a second fuel passage), which isconnected to the control chamber 11 of the booster 3 is provided with ahydraulic pressure valve 18, and an outflow passage 52 (a first fuelpassage) is provided with a check valve 17. The inflow passage 51 is afuel passage for transmitting the fuel pressure in the accumulator 2 tothe control chamber 11. As shown in FIG. 9, the inlet port 45 of thehydraulic pressure valve 18 is connected to the accumulator 2, and theoutlet port 46 is connected to the control chamber 11. The outflowpassage 52 is a fuel passage for releasing the fuel pressure in thecontrol chamber 11 to the lower pressure side. As shown in FIG. 9, theoutflow passage 52 connects the control chamber 11 to the switching port40 of the control valve 5.

The hydraulic pressure valve 18, which is provided in the inflow passage51, is in the valve opening mode (a state shown in FIG. 9) to open theinflow passage 51 when the control valve 5 is in the fuel pressuretransmission mode. The hydraulic pressure valve 18 is in the valveclosing mode to block the inflow passage 51 when the control valve 5 isin the fuel pressure release mode. The check valve 17, which is providedin the outflow passage 52, allows a fuel flow from the control chamber11 to the control valve 5, and prevents a backward fuel flow. Thus, whenthe control valve 5 is set to the fuel pressure transmission mode, thefuel pressure in the accumulator 2 is transmitted via the inflow passage51 to the control chamber 11. When the control valve 5 is switched tothe fuel pressure release mode, the fuel pressure in the control chamber11 is released via the outflow passage 52 to the lower pressure side, tostart the pressure increase operation of the booster 3.

In the third embodiment, the pressure transmission path 48, which isconnected to the operation chamber 18 d of the hydraulic pressure valve18 (refer to FIG. 2), is provided with the aperture 49. By an effect ofthe aperture 49 and/or an operation pressure of the hydraulic pressurevalve 18, it is possible to apply a time lag to a timing to startoperating the booster 3 (to start the pressure increase), in the samemanner as in the first embodiment.

In the third embodiment, it is possible to improve a flexibility in thepressure decreasing step including a pressure increase completiontiming. It is also possible to equalize the injection start timing andpressure increase start timing approximately with each other. Thus, itis possible to start pressure increase from an initial time, to derive atriangular shaped injection ratio pattern in a wave form of theinjection ratio.

Fourth Embodiment

FIG. 10 depicts a hydraulic circuit of a fuel injection apparatus 1according to a fourth embodiment of the present invention.

In the fuel injection apparatus 1 according to the fourth embodiment,the control chamber 11 of the booster 3 is directly connected via onefuel passage 53 to the switching port 40 of the control valve 5. Theswitching port 40 of the control valve 5 is connected by two fuelpassages 54, 55 in parallel to the back pressure chamber 25 of thenozzle 4.

The fuel passage 54 (a first fuel passage) is provided with the checkvalve 17, which allows a fuel from the control valve 5 to the backpressure chamber 25, and prevents a backward fuel flow. The fuel passage55 (a second fuel passage) is provided with the hydraulic pressure valve18. The hydraulic pressure valve 18 is in the valve closing mode (astate shown in FIG. 10) to block the fuel passage 55 when the controlvalve 5 is in the fuel pressure transmission mode. The hydraulicpressure valve 18 is in the valve opening mode to open the fuel passage55 when the control valve 5 is in the fuel pressure release mode.

In the fourth embodiment, the pressure transmission path 48, which isconnected to the operation chamber 18 d of the hydraulic pressure valve18 (refer to FIG. 2), is provided with the aperture 49. By an effect ofthe aperture 49 and/or an operation pressure of the hydraulic pressurevalve 18, it is possible to apply a time lag to a timing to startoperating the booster 3 (to start the pressure increase), in the samemanner as in the first embodiment.

By the construction according to the fourth embodiment, when the controlvalve 5 is switched from the fuel pressure transmission mode to the fuelpressure release mode, the fuel pressure in the control chamber 11 ofthe booster 3 immediately starts decreasing to start pressure increasein the booster 3. Then, the hydraulic pressure valve 18 starts operating(is switched from the valve closing mode to the valve opening mode) witha time lag, and the fuel pressure in the back pressure chamber 25decreases to start fuel injection. Thus, it is possible to inject thefuel at the super high pressure from an injection start, to derive apulse shaped injection ratio pattern.

When the fuel injection completes, the control valve 5 is switched tothe fuel pressure transmission mode, so that the pressure increasingoperation of the booster 3 immediately stops. Concurrently, a highpressure, that is, the fuel pressure in the accumulator 2 is transmittedvia the one fuel passage 54 having the check valve 17 to the backpressure chamber 25, so that the fuel injection rapidly stops. Thiseffect is achieved not by the hydraulic pressure valve 18, which startsoperating with a time lag. The rapid fuel injection stop is effectivefor decreasing a black smoke emitted from the internal combustionengine.

This description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

1. A fuel injection apparatus for an internal combustion enginecomprising: an accumulator for accumulating fuel therein at apredetermined pressure; a booster provided with a control chamber inwhich fuel pressure changes in accordance with a fuel inflow into thecontrol chamber and a fuel outflow out of the control chamber, and ahydraulic piston that moves in accordance with a change of the fuelpressure in the control chamber, the booster pressurizing the fuelsupplied from the accumulator in accordance with a pressurizingoperation of the hydraulic piston; a nozzle provided with a backpressure chamber in which fuel pressure changes in accordance with afuel inflow into the back pressure chamber and a fuel outflow out of theback pressure chamber, and a needle that moves in accordance with achange of the fuel pressure in the back pressure chamber, the nozzleinjecting the fuel supplied from the accumulator or the fuel pressurizedby the booster in accordance with a valve opening operation of theneedle; a hydraulic circuit provided with a fuel passage fortransmitting the fuel pressure in the accumulator to the control chamberand to the back pressure chamber, and a fuel passage for releasing thefuel pressure in the control chamber and in the back pressure chamber toa low pressure system; a hydraulic pressure valve provided with a valvebody that is disposed in a fuel passage communicated with the controlchamber or disposed in a fuel passage communicated with the backpressure chamber to open and block the fuel passage to control anoperation of the valve body in accordance with the fuel pressure that istransmitted via a transmission path connected to the hydraulic circuit;and a control valve provided with a valve body that is driven by atwo-position actuator, the valve body connecting any one of a highpressure side communicated the accumulator and the low pressure systemcommunicated with a fuel tank to the hydraulic circuit, to control thehydraulic circuit, and to control the fuel pressure transmitted to thehydraulic pressure valve, one of the fuel pressure in the controlchamber and the fuel pressure in the back pressure chamber beingdirectly controlled by the control valve, and the other of the fuelpressure in the control chamber and the fuel pressure in the backpressure chamber being indirectly controlled via the hydraulic pressurevalve, to control an operation of the booster and an operation of thenozzle, wherein at least one of the transmission path and the hydraulicpiston is configured to generate a delay in an operation of the nozzleor the booster that is driven by the other of the fuel pressure in theback pressure chamber and the fuel pressure in the control chamberindirectly controlled by the hydraulic pressure valve, against anoperation of the booster or the nozzle that is driven by the one of thefuel pressure in the control chamber and the fuel pressure in the backpressure chamber directly controlled by the control valve.
 2. The fuelinjection apparatus for an internal combustion engine according to claim1, wherein the transmission path is provided with an aperture togenerate the delay.
 3. The fuel injection apparatus for an internalcombustion engine according to claim 1, wherein an operation pressure ofthe hydraulic piston is set to a value to generate the delay.
 4. Thefuel injection apparatus for an internal combustion engine according toclaim 1, wherein the transmission path is provided with an aperture andan operation pressure of the hydraulic piston is set to a value togenerate the delay.
 5. The fuel injection apparatus for an internalcombustion engine according to claim 1, wherein the control valve isprovided with: a switching port connected to the hydraulic circuit; aninput port communicated with the accumulator; and a low pressure portconnected to a drain passage at a side of the low pressure system, andthe valve body of the control valve is a two-position three way valvethat selectively switches between a fuel pressure transmission mode inwhich the valve body blocks a communication between the low pressureport and the switching port and allows a communication between the inputport and the switching port, and a fuel pressure release mode in whichthe valve body blocks the communication between the input port and theswitching port and allows the communication between the low pressureport and the switching port.
 6. The fuel injection apparatus for aninternal combustion engine according to claim 1, wherein the hydraulicpressure valve is a two-position two way valve.
 7. The fuel injectionapparatus for an internal combustion engine according to claim 1,further comprising two fuel passages connecting the control valve inparallel with the control chamber, one of the fuel passages beingprovided with a fuel flow direction restriction means that allows a fuelflow from the control valve to the control chamber and prevents a fuelflow from the control chamber to the control valve, and the other of thefuel passages being provided with the hydraulic pressure valve.
 8. Thefuel injection apparatus for an internal combustion engine according toclaim 1, further comprising: a first fuel passage that connects thecontrol chamber to the control valve and is provided with a fuel flowdirection restriction means that allows a fuel flow from the controlvalve to the control chamber and prevents a fuel flow from the controlchamber to the control valve; and a second fuel passage that connectsthe control chamber to a drain passage at a side of the low pressuresystem and is provided with the hydraulic pressure valve.
 9. The fuelinjection apparatus for an internal combustion engine according to claim1, further comprising: a first fuel passage that connects the controlchamber to the control valve and is provided with a fuel flow directionrestriction means that allows a fuel flow from the control chamber tothe control valve and prevents a fuel flow from the control valve to thecontrol chamber; and a second fuel passage that connects the controlchamber to the accumulator and is provided with the hydraulic pressurevalve.
 10. The fuel injection apparatus for an internal combustionengine according to claim 1, further comprising two fuel passagesconnecting the control valve in parallel with the back pressure chamber,one of the fuel passages being provided with a fuel flow directionrestriction means that allows a fuel flow from the control valve to theback pressure chamber and prevents a fuel flow from the back pressurechamber to the control valve, and the other of the fuel passages beingprovided with the hydraulic pressure valve.
 11. The fuel injectionapparatus for an internal combustion engine according to claim 1,wherein the hydraulic pressure valve is operated by a pressuredifference between the fuel pressure transmitted from the transmissionpath and the fuel pressure in the accumulator.
 12. The fuel injectionapparatus for an internal combustion engine according to claim 1,wherein the fuel passage communicated with the back pressure chamber isprovided with an aperture, an opening degree of the aperture variablydetermining a moving speed of the needle.
 13. The fuel injectionapparatus for an internal combustion engine according to claim 1,wherein the fuel passage communicated with the control chamber isprovided with an aperture, an opening degree of the aperture variablydetermining a moving speed of the hydraulic piston.
 14. The fuelinjection apparatus for an internal combustion engine according to claim1, wherein the fuel passage communicated with the back pressure chamberand the fuel passage communicated with the control chamber arerespectively provided with apertures, opening degrees of the aperturesvariably determining a moving speed of the needle and a moving speed ofthe hydraulic piston.